An image forming apparatus employing an electrostatic electrophotographic printing method performs the steps of: charging, exposure, development, transfer, separation, cleaning, and fixation, so as to form an image on a transfer material (recording material) such as paper. Specifically, a surface of a photoreceptor drum which is driven to rotate by a charging device is uniformly charged (charging). Then, a laser beam is directed, by an exposure device, toward the photoreceptor drum thus charged, whereby an electrostatic latent image is formed (exposure) on the photoreceptor drum. Subsequently, the electrostatic latent image on the photoreceptor drum is developed by a developing device so that a toner image is formed on the surface of the photoreceptor drum (development). Then, the toner image on the photoreceptor drum is transferred to the transfer material by a transfer device (transfer). Thereafter, the toner image is heated by a fixing device, whereby the toner image is fixed onto the transfer material (fixation).
A developer for developing the electrostatic latent image on the photoreceptor drum is a single component developer containing only a toner or a two component developer containing the toner and a carrier. The single component developer requires no stirring system in which the toner and the carrier are mixed together and thus the developing device has a simple structure. However, on the other hand, the single component developer has at least a problem that a charge amount of the toner is less likely to be stable. In contrast, the two component developer requires a stirring system in which the toner and the carrier are mixed together. However, according to the two component developer, the charge amount of the toner is highly likely to be stable and it is therefore possible to obtain a high-definition image.
However, there occurs a problem that long-term use of the two component developer causes a surface of the carrier to be worn, thereby leading to a change in electric resistance and charge property. The change in electric resistance and charge property causes a deterioration in image quality. In order to solve this problem, the carrier is coated with a coating resin, so as to cause the surface of the carrier to be more wear-resistant. However, even if the surface of the carrier is coated with the coating resin as described above, the two component developer still has a shorter lifetime as compared to the image forming apparatus. For this reason an old two component developer (carrier) which has reached its lifetime is replaced with a new two component developer (carrier), whereby the deterioration in image quality is prevented.
Note that from an environmental viewpoint, reuse of an old carrier is suggested so that a smaller amount of a used carrier is disposed of. For example, Patent Literature 1 discloses a carrier regenerating method in which a coating resin of a used carrier is removed by hydrolysis and thereafter resulting core particles are coated with the coating resin.